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            "title": "Construct Quad Tree",
            "titleSlug": "construct-quad-tree",
            "content": "<p>Given a <code>n * n</code> matrix <code>grid</code> of <code>0&#39;s</code> and <code>1&#39;s</code> only. We want to represent the <code>grid</code> with a Quad-Tree.</p>\n\n<p>Return <em>the root of the Quad-Tree</em> representing the <code>grid</code>.</p>\n\n<p>Notice that you can assign the value of a node to <strong>True</strong> or <strong>False</strong> when <code>isLeaf</code> is <strong>False</strong>, and both are <strong>accepted</strong> in the answer.</p>\n\n<p>A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides, each node has two attributes:</p>\n\n<ul>\n\t<li><code>val</code>: True if the node represents a grid of 1&#39;s or False if the node represents a grid of 0&#39;s.</li>\n\t<li><code>isLeaf</code>: True if the node is leaf node on the tree or False if the node has the four children.</li>\n</ul>\n\n<pre>\nclass Node {\n    public boolean val;\n    public boolean isLeaf;\n    public Node topLeft;\n    public Node topRight;\n    public Node bottomLeft;\n    public Node bottomRight;\n}</pre>\n\n<p>We can construct a Quad-Tree from a two-dimensional area using the following steps:</p>\n\n<ol>\n\t<li>If the current grid has the same value (i.e all <code>1&#39;s</code> or all <code>0&#39;s</code>) set <code>isLeaf</code> True and set <code>val</code> to the value of the grid and set the four children to Null and stop.</li>\n\t<li>If the current grid has different values, set <code>isLeaf</code> to False and set <code>val</code> to any value and divide the current grid into four sub-grids as shown in the photo.</li>\n\t<li>Recurse for each of the children with the proper sub-grid.</li>\n</ol>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/11/new_top.png\" style=\"width: 777px; height: 181px;\" />\n<p>If you want to know more about the Quad-Tree, you can refer to the <a href=\"https://en.wikipedia.org/wiki/Quadtree\">wiki</a>.</p>\n\n<p><strong>Quad-Tree format:</strong></p>\n\n<p>The output represents the serialized format of a Quad-Tree using level order traversal, where <code>null</code> signifies a path terminator where no node exists below.</p>\n\n<p>It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list <code>[isLeaf, val]</code>.</p>\n\n<p>If the value of <code>isLeaf</code> or <code>val</code> is True we represent it as <strong>1</strong> in the list <code>[isLeaf, val]</code> and if the value of <code>isLeaf</code> or <code>val</code> is False we represent it as <strong>0</strong>.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/11/grid1.png\" style=\"width: 777px; height: 99px;\" />\n<pre>\n<strong>Input:</strong> grid = [[0,1],[1,0]]\n<strong>Output:</strong> [[0,1],[1,0],[1,1],[1,1],[1,0]]\n<strong>Explanation:</strong> The explanation of this example is shown below:\nNotice that 0 represnts False and 1 represents True in the photo representing the Quad-Tree.\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e1tree.png\" style=\"width: 777px; height: 186px;\" />\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<p><img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e2mat.png\" style=\"width: 777px; height: 343px;\" /></p>\n\n<pre>\n<strong>Input:</strong> grid = [[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,1,1,1,1],[1,1,1,1,1,1,1,1],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0],[1,1,1,1,0,0,0,0]]\n<strong>Output:</strong> [[0,1],[1,1],[0,1],[1,1],[1,0],null,null,null,null,[1,0],[1,0],[1,1],[1,1]]\n<strong>Explanation:</strong> All values in the grid are not the same. We divide the grid into four sub-grids.\nThe topLeft, bottomLeft and bottomRight each has the same value.\nThe topRight have different values so we divide it into 4 sub-grids where each has the same value.\nExplanation is shown in the photo below:\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/02/12/e2tree.png\" style=\"width: 777px; height: 328px;\" />\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>n == grid.length == grid[i].length</code></li>\n\t<li><code>n == 2<sup>x</sup></code> where <code>0 &lt;= x &lt;= 6</code></li>\n</ul>\n",
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                    "code": "/*\n// Definition for a QuadTree node.\nclass Node {\npublic:\n    bool val;\n    bool isLeaf;\n    Node* topLeft;\n    Node* topRight;\n    Node* bottomLeft;\n    Node* bottomRight;\n    \n    Node() {\n        val = false;\n        isLeaf = false;\n        topLeft = NULL;\n        topRight = NULL;\n        bottomLeft = NULL;\n        bottomRight = NULL;\n    }\n    \n    Node(bool _val, bool _isLeaf) {\n        val = _val;\n        isLeaf = _isLeaf;\n        topLeft = NULL;\n        topRight = NULL;\n        bottomLeft = NULL;\n        bottomRight = NULL;\n    }\n    \n    Node(bool _val, bool _isLeaf, Node* _topLeft, Node* _topRight, Node* _bottomLeft, Node* _bottomRight) {\n        val = _val;\n        isLeaf = _isLeaf;\n        topLeft = _topLeft;\n        topRight = _topRight;\n        bottomLeft = _bottomLeft;\n        bottomRight = _bottomRight;\n    }\n};\n*/\n\nclass Solution {\npublic:\n    Node* construct(vector<vector<int>>& grid) {\n        \n    }\n};",
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                    "code": "/*\n// Definition for a QuadTree node.\nclass Node {\n    public boolean val;\n    public boolean isLeaf;\n    public Node topLeft;\n    public Node topRight;\n    public Node bottomLeft;\n    public Node bottomRight;\n\n    \n    public Node() {\n        this.val = false;\n        this.isLeaf = false;\n        this.topLeft = null;\n        this.topRight = null;\n        this.bottomLeft = null;\n        this.bottomRight = null;\n    }\n    \n    public Node(boolean val, boolean isLeaf) {\n        this.val = val;\n        this.isLeaf = isLeaf;\n        this.topLeft = null;\n        this.topRight = null;\n        this.bottomLeft = null;\n        this.bottomRight = null;\n    }\n    \n    public Node(boolean val, boolean isLeaf, Node topLeft, Node topRight, Node bottomLeft, Node bottomRight) {\n        this.val = val;\n        this.isLeaf = isLeaf;\n        this.topLeft = topLeft;\n        this.topRight = topRight;\n        this.bottomLeft = bottomLeft;\n        this.bottomRight = bottomRight;\n    }\n};\n*/\n\nclass Solution {\n    public Node construct(int[][] grid) {\n        \n    }\n}",
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                    "code": "\"\"\"\n# Definition for a QuadTree node.\nclass Node(object):\n    def __init__(self, val, isLeaf, topLeft, topRight, bottomLeft, bottomRight):\n        self.val = val\n        self.isLeaf = isLeaf\n        self.topLeft = topLeft\n        self.topRight = topRight\n        self.bottomLeft = bottomLeft\n        self.bottomRight = bottomRight\n\"\"\"\n\nclass Solution(object):\n    def construct(self, grid):\n        \"\"\"\n        :type grid: List[List[int]]\n        :rtype: Node\n        \"\"\"\n        ",
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                    "code": "/**\n * // Definition for a QuadTree node.\n * function Node(val,isLeaf,topLeft,topRight,bottomLeft,bottomRight) {\n *    this.val = val;\n *    this.isLeaf = isLeaf;\n *    this.topLeft = topLeft;\n *    this.topRight = topRight;\n *    this.bottomLeft = bottomLeft;\n *    this.bottomRight = bottomRight;\n * };\n */\n\n/**\n * @param {number[][]} grid\n * @return {Node}\n */\nvar construct = function(grid) {\n    \n};",
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                    "code": "# Definition for a QuadTree node.\n# class Node\n#     attr_accessor :val, :isLeaf, :topLeft, :topRight, :bottomLeft, :bottomRight\n#     def initialize(val=false, isLeaf=false, topLeft=nil, topRight=nil, bottomLeft=nil, bottomRight=nil)\n#         @val = val\n#         @isLeaf = isLeaf\n#         @topLeft = topLeft\n#         @topRight = topRight\n#         @bottomLeft = bottomLeft\n#         @bottomRight = bottomRight\n#     end\n# end\n\n# @param {Integer[][]} grid\n# @return {Node}\ndef construct(grid)\n\t\nend",
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                    "code": "/**\n * Definition for a QuadTree node.\n * public class Node {\n *     public var val: Bool\n *     public var isLeaf: Bool\n *     public var topLeft: Node?\n *     public var topRight: Node?\n *     public var bottomLeft: Node?\n *     public var bottomRight: Node?\n *     public init(_ val: Bool, _ isLeaf: Bool) {\n *         self.val = val\n *         self.isLeaf = isLeaf\n *         self.topLeft = nil\n *         self.topRight = nil\n *         self.bottomLeft = nil\n *         self.bottomRight = nil\n *     }\n * }\n */\n\nclass Solution {\n    func construct(_ grid: [[Int]]) -> Node? {\n        \n    }\n}",
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